Resonant circuit saturable core measurement apparatus



Dec. 3, 1946. 2,412,046

RESONAN'I cmcun' SATURABLE CORE MEASUREMENT APPARATUS s. c. oARE Filed Sept. 8, 1943 FREQUENCY $0 CYCLES Inventor: Stepheh C.Hoar-e,

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Hus Attorney.

in which it is desired to measure the current.

Patented Dec. 3,

BESONANT CIRCUIT SATURABLEbORE I I MEASUREMENT APPARATUS Stephen C. Hoare, Manchester, Mam, asei g'nor to General Electric Company. a

New York corporation of Application September a, 1943. sci-lame. 501,549

1 My invention relates to unidirectional flux saturable core measuring apparatus and circuits, and its object is to provide such apparatus of high sensitivity and amplifying ability. An important aspect 01' my invention is the use of a tuned circuit or circuits in which there is included, as a variable inductance, a saturable core. Where two tuned circuits are employed, a diil'erential amplifying efiect may be obtained by operation of the two circuits on diflerent slopes or inreverse direction on the same slope of their resonant curves over the detecting or measuring range. These and other features of my invention will be explained in connection with the accompanying drawing, while the features which are considered to be novel and patentable will be pointed out in the claims -appended hereto.

' Fig. 1 represents a simple embodiment of my invention involving a resonant circuit inwhich a change in tuning isvobtained by a saturable core reactor. Fig. 2 shows resonant curves explanatory of Fig. 1. Fig. 3 shows an arrangement where a pair of saturable core resonant circuits are em- 4Clalms. (01. 175-183) ployed differentially. Figs. 4 and 5 are resonant curves explanatory oi the arrangement of Fig. 3. Fig. 6 represents a compass application of my invention where the degree of saturation is con trolled by the earths field. Figs. 7 and 8 are resonance curves explanatory of Fig 6, and Fig. 9 represents a further embodiment of my invention where the difl'erential resonant circuit principle is combined with a push-pull alternating current excitation amplifier scheme. I

In Fig. 1 let i0 represent a'direct' current circuit H represents a saturable-core of high permeability magnetic material having a, low saturation point, such for example, as mu metal. This core is magnetized by unidirectional flux in proportion to the direct current to be measured by a winding 12 connected across a shunt IS in the circuit I0. I 4 represents another winding on core Ii energized by alternating current from a source l5.. The winding i4 is in series with a condenser l6 and an alternating current responsive instrument II. It is seen that the alternating current circuit contains an inductance H which is varied by the degree of saturation of the core II, and the condenser 5 which may also be variable for calibration purposes. However, the saturable core inductance is the measurement variable of the A. C. circuit. The circuit will also contain some resistance, and the sharpness of the resonance curve of the circuit will depend upon the amount of resistance therein. a

I 2 Q It is known that anarrangement similar to that here shown in Fig. 1, omitting the condenser I.

the variation in the inductance of the alternating current circuit by-various degrees of saturation of the core ll. However, when the alternatin current circuit is tuned by means of a condenser and the circuit is properly used .over the slope of the resonance curve, a large increase in sensitivity is obtained. Let it be assumed that with no direct current flowing in coil l2, the alternating current circuit has a resonant curve a, Fig. 2, and operates at the point a: of such curve for the frequency 01' source iii which is assumed to be constant at 60 cycles. Hence, at such time a current :6 will flow in instrument ll, but its indication may be suppressed as, for example, by adjustment of the zero return spring so as to have-a scale-reading of zero. Now with direct current flowing in coil l2, corresponding to the upper limitof the direct current to be measured, the circuit con-. stants can be so arranged that resonant curve characteristic of the alternating current circuit will be represented by curve b, because due to saturation of core i I the inductance in the alternating current circuit has been decreased, and hence, the alternating current circuit will be, tuned to resonance at a higher frequency than before.

, However, the frequency remains constant, so that a current 11 now. flows in the instrument ll. I have found that the sensitivity of the arrangement can thus be greatly increased by simply addingth'e condenser and taking advantage of the resonant principle.

In Fig. 3, I have provided two saturable cores l8 and I9 each provided with saturating direct same direction. The same eflect would beob tained if the direct current coils, were wound the same and the alternating windin s were wound in opposite directions. l

I'n,the arrangement of Fig, Li when therefisnq i e w r n win t al c atinai current;

circuitsare so adjusted that theclr'cuit contaim ing winding 22 and condenser 24 operates at about the midpoint of the high irequency slope of its resonance curve as at point 1:, curve 0, Fig. 4, while the circuit containing winding 23 and condenser 25 operates at about the midpoint of the low frequency slope oi its resonance curve as at point 1:, curve 11, Fig. 5, and iurther, so that equal currents a: flow in the parallel alternating current circuits. Under these conditions it will be apparent that the voltage across which the rectifier instrument is connected will be zero. and no current will flow in the rectifier instrument. Now when direct current flows in windings 23 and 2| to more or less saturate the cores i3 and IS, the reactances oi. the alternating current circuits will decrease and at the upper limit of direct current fiow the resonance curve 01' the alternating current circuit containing winding 22 will be represented by curve e, Fig, 4, and carry an increased current 1:, while the resonance curve oi the circuit containing winding 23 will be represented as at f. Fig. 5, and carry a decreased current 2. Note that despite saturation of core I9, the current in its alternating current winding circuit decreases because of a further departure from a resonance condition. The voltages across windings 22 and 23 will be proportional to the difference in the currents y-z flowing therethrough, and this voltage is impressed across the rectifier instrument 2!! and produces a corresponding ilow of direct current therethrough. It is seen then that the indication of the rectifier instrument will be proportional to the direct current flowing in circuit H), but the amplifying ability or sensitivity of the measuring arrangement will be increased many times over nonresonant saturable core measuring schemes of the prior art.

In Fig. 6, I have shown a modification of my invention as adapted for a remote indicating magnetic direction indicator where the variable saturation efl'ect is controlled by the earth's field. In Fig. 6 the core parts l8 and I9 are to be located so as to pick up the earth's field. For instance, they may be located on the wing of an airplane sufficiently remote from other magnetic material and disturbing influences to respond accurately to the direction and strength of the earth's field, and with their alternating current windings connected with a remote indicator 2! arranged to indicate the direction in which the airplane is headed. The core parts [8 and [9 are of such dimensions and material as to become partially saturated by the earths field when turned in line therewith, with the turning of the airplane or other structure to which they are fixed. The earths field takes the place of the direct current windin s 20 and 2| of Fig. 3, and there are in addition, biasing direct current windlugs 23 and 29 wound oppositely on the two cores and connected in series to a direct current source 30 through an adjustable rheostat 3| The alternating current windings 22 and 23 and the condensers 24 and 25 in series therewith correspond to like elements in Fig. 3. The instrument 2'! is shown as a ratio instrument having coils 32 and 33 connected to measure the ratio of currents in the parallel alternating current tuned circuits. This instrument can be either alternating current or rectifier direct current so long as it responds to the ratio oi the al-temating currents.

In the illustration it is assumed that the upper ends of the core parts l3 and H are toward the magnetic north, and therefore, picking up a maximum amount oi the earth's field in a given direction.

The adjustment oi the apparatus is as iollows: When the earth's flux pickup strips l8 and I! are turned in an east-west direction so as to pick up none of the earth's magnetic field, the current in coils 28 and 23 is adjusted so that the strips I8 and I9 are partially saturated and the condensers 24 and 25 are adjusted so that the circuit oi. condenser 24 operates at point 11:, curve la, Fig. 7, and the circuit oi condenser 25 operates at point 3:: on curve 8a, Fig. 8.- At this. time, then, the currents in coils 32 and 33 are equal and the instrument 2! has a central deflection and indication opposite the designation E-W, indicating that the ship is headed either west or east. Inasmuch as this condition will prevail when the strips I 8 and I3 are at right angles to the earth's fie1d,-the instrument 2! will not, by itself, indicate whether the ship is headed east or west, so that I provide a small, cheap compass 34 which will point toward the designations E or W depending upon the heading. The accuracy of compass 34 needs to be sufllcient only to distinguish between east and west. Now let us assume the ship is headed to true magnetic north, so that the pickup strips I 8 and I! will pick up maximum earth's flux in a driven direction. The direction of current in coil 23 oi strip l9 is'such as to add its flux to the earth's flux in strip [9 at this time and to increase the saturation of such strip, decreasing the inductance of the corresponding alternating current circuit and causing it to have a resonance curve 8b and a current 3; Fig. 8. The current in coil 28, however, is in such direction as to oppose the earth's flux picked up by strip i8, 50 that the saturation of this strip is decreased and its corresponding alternating current circuit now operates at point 11/, curve lb, Fig. 7. The ratio instrument 2! thus measures the ratio of currents cuits will operate on resonant curves 1c and 8c with currents Ia and 82:, respectively, Figs. 7 and 8. Under this condition coil 32 will predominate and the instrument will indicate 8. For intermediate headings the instrument will have intermediate indications, and the scale may be calibrated in direction angles accordingly. If the apparatus is used in widely difierent localities such that the strength of the earth's field varies appreciably, recalibration for the diiierent conditions will be called for.

The push-pull feature of Fig. 6 represents an improvement even without utilizing the resonant features. However, including the resonant principles described very materially increases the sensitivity. It is to be understood that the nature of the instrument or other devic of 21, Fig. 6, may be any instrumentality which will respond to the current flow in the parallel alternating current circuits to give a signal or response in south, coil 28 ment of Fig. 3 or 6 may be further increased by a dififerential inductive coupling between-the par-.

allel alternating current circuits and the saturabl cores employed as represented in Fig. 9. Except for the additional alternating current windings 36 and 31 in Fig. 9, the arrangement is equivcircuit of alternating current winding 22 on core I8 hasa low turn winding 31 on core l9 wound in opposition to main alternating current current and alternating current windings on one core being similarly wound and those on the other core being reverseiy wound, a common source of alternating current supply for said parallel circults, said circuits being so tuned that corresponding changes in the unidirectional flux inthe pair of core parts cause the current in one circuit to increase and the current in the other circuit to decrease, and means associated with both of 10 saidrtuned circuits responsive to th differential currentfiow in said parallel circuits.

2. Unidirectional flux responsive apparatus I comprising apair of magnetic coreparts so disposed as to intercept unidirectional flux under investigation and to be subject to varying degrees winding 23 thereon. This arrangement causes the effective alternating current excitingampere turns to change faster than the change in alternating current exciting current. Let it be assumed that coils 22 and 23 each have 100 turns and coils '36 and 31 have turns and that when the currents in the two alternating current circuits are equal; one ampere flows in each circuit. Then the effective alternating current ampere turns in each alternating current circuit are 1oo-2o=ao.. Now assume that because of a difl'erent condition of saturation, the alternating current exciting current of winding 22 increases by 10 per cent and that of winding 23 decreases by 10 per cent. Then the eflective ampere turns in branch 2: become 11018=92, and the eii'ec tive ampere turns in branch :3 become 90-22 .88.

Thus the 10 per cent change inexciting current causes a 15 per cent chang in effective ampere turns in the differentially coupled alternating current circuits. The reactance in each alternating current circuit branch .is proportional to the eil'ective alternating current ampere turns. Hence, a change in saturation influencing the reactance or effective ampere turns-is amplified by such dinerential or cross-coupling or the alternating current circuits. This isin addition to the amplification obtained by the dlflerential resonance principle employed. By the proper use of the diil'erential resonance principle and of magnetic saturation by variations in the magnitude of the fiuxintercepted, awinding on each of. said core parts, means for connecting said windings in parallel circuits to an alternating current supply. means including said windings for tuning said circuits such that corresponding changes in the magnitude of unidirectional flux intercepted by said core parts will cause the currents in the parallel circuits to'vary inversely,

and means responsive to the differential current flow in said circuits.

3. Unidirectional flux responsive apparatus subject to magnetic fields comprising a pair of elongated magnetic core parts mounted parallel to each other, direct current winding means on said core parts for producing reverse unidirec- -tional flux biases in said core parts such that when in line with a unidirectional magnetic field such field, with the biasing flux, will substantlally saturate one core part and substantially demagnetize the other core art, alternating current windings onsaid core parts, means for .connecting said windings in parallel circuits to an alternating current source of supply, means includlng said windings -ior tuning said parallel circuits such that said circuits operate on sim- 5 mea'ns responsive t the current flow in said the diil'erential coupling oi the alternating current circuits, an amplification oi the order of six times the sponse'oi' the ordinary saturable core arrangement may be realized.

' In accordance with the provisions of the patent statutes, I have described the principle of operation oi'.my invention together with theapparatus -whichI now consider to represent the best em- Letters Patent of the United States is:

- L-Unidirectional ilux responsive apparatus parallel circuits to give a signal in accordance with the ratio of the currents in said parallel circuits.

4. Unidirectional flux responsive apparatus comprising a pair of magnetic core parts adapted to intercept unidirectional flux under investigation and to be subject 'to various degrees of saturation-by variations in the flux intercepted, a

main exciting winding and an auxiliary bucking winding on each core part,'a tuned circuit ineluding the main winding-on one core part and the auxiliary bucking winding on the other core part, asecond tuned, circuit including the remaining windings on the core parts, connections for energizing both of said circuits in parallel comprising a pair of magnetic core parts adapted .to be threaded by the flux under investigation and to be subject to varying degrees of saturation from a common source of alternating current supply. the tuning of said circuits being such as to cause their currents to vary inversely with respect to each'other by similar changes in the by changes in the unidirectional flux threading as fluxes intercepted by the core parts, and means saidcore parts, a pair oi windings energised currentv on said cores. 0. pair of parallel timed circuits'including alternating current excitinrwindings on said core parts, the direct associated .with both of said tuned circuits responsive to'the relative magnitude of current fiow in said parallel circuits. C. BOAR. 

